Double Mode Pulsation as a Resonance Phenomenon

It is proposed that the maintenance of stable double-mode pulsation involves a resonant interaction between the two excited modes. This hypothesis yields a simple explanation of the narrow range of period ratio (P1/P0) observed in both the double-mode Cepheids and the double-mode AI Velorum stars. The resonance idea is consistent with the under-massive models previously invoked to match the double-mode Cepheids, but seems to rule out normal Population I masses for the AI Velorum stars. It is argued that observational evidence regarding the pulsations of the AI Vel objects does not at present preclude the latter result